1. Field of the Invention
The present invention relates to an apparatus and a method for estimating edge areas of pixels in a digital image, and more particularly, to an apparatus and a method for estimating edge areas of pixels in a digital image to thereby prevent an edge sharpening algorithm from being applied to non-edge area of the digital image.
2. Description of the Related Art
In general, the light sense of humans tends to prefer images with high-definition in recognizing images displayed on an image device. Various techniques for improving the definition of an image have been applied to an image device, such as a digital camera, a TV, and a camera-mounted mobile phone, so as to meet the preference of the light sense of humans. One of the techniques for improving image definition is to make the edge (outline) of a digital image sharper.
As for well-known edge sharpening techniques in the related art, two techniques are broadly used. One of the two techniques is based on the fact that a filtering value, generated by applying two-dimensional High Pass Filtering (2D-HPF) to the whole image, is applied to an original image. The other is based on the fact that a filtering value is applied to an original image, the filtering value being generated by applying a 2D-HPF according to characteristics (e.g., directivity) of the edge of an image.
In the case of the former, the 2D-HPF is applied to the entire image, and then the resultant image is added to an original image. However, excessive sharpening is made on the strong edge, and thus overshooting and undershooting occur, which results in a ringing phenomenon in which white border is formed within a border of an object. Also, internal noise of an image device makes shaken parts (background noise), represented on a flat area of an image, sharper, and thus the image is unnatural.
In the case of the latter, directivity (i.e., one of characteristics of an edge of an image) is identified, and then a 2D-HFP process, suitable for determining the directivity of each edge is selectively applied thereto. That is, the directivity of each edge, such as horizontal, vertical, and diagonal directions, as well as non-directivity, is identified, and then a 2D-HPF process suitable for each of the directivities is selectively applied thereto, to generate a filtering value and apply the filtering value to an input image. In the technique, the more the kind of directivities of edges, the more 2D-HDFs is required depending on various factors (type of determination equation, priority for determination's result, and directivity). Therefore, a system for performing edge sharpening becomes larger. Also, in the case of the latter, the directivity of an edge is identified, but the magnitude of the edge is not considered, so a ringing phenomenon may occur on strong edges, as in the case of the former sharpening. Also, each pixel of an image is subjected to 2D-HPF filtering depending on its directivity, and thus edge sharpening is discontinuous, which results in a reduction of definition of an image. Therefore, in the prior art, in order to improve the definition of a digital image, there is required a technique for estimating edges as a solution for solving an image of low quality by applying edge sharpening to unnecessary portions.
Therefore, in order to solve the conventional problem of a degradation in an image's quality due to unnecessary edge sharpening, there is required a technique for estimating edge areas to improve the definition of a digital image.